The invention relates to a process for producing gaseous crude argon by low-temperature rectification of air wherein air is compressed, prepurified, cooled, and fed into a high-pressure stage of a two-stage rectification and wherein crude argon in the liquid phase is obtained downstream of the two-stage rectification.
Such a process is disclosed in DOS No. 3,428,968. Crude argon is withdrawn in the liquid phase from the head of a crude argon column or is liquefied after removal from a crude argon column. The liquid crude argon is subjected to a pressure increase, utilizing its hydrostatic potential, in order to raise the pressure of the crude argon, generally obtained under approximately atmospheric pressure, to the pressure of about 3.5-5 bar required for further processing. This mode of operation offers the saving advantage of eliminating the cost of a separate compressor for compression of the crude argon--required, for example, in the case of gaseous withdrawal of crude argon.
The crude argon, which is under elevated pressure, must be vaporized for obtaining pure argon. The refrigeration produced by evaporation is removed by heat exchange with nitrogen in the process of DOS No. 3,428,968. However, in the case of a low-pressure facility wherein the air is compressed to about 6 bar, such a process stream is not available under a sufficiently high enough pressure to result in the nitrogen being liquefied by heat exchange with the crude argon to be vaporized under elevated pressure. Thus, merely the sensible heat (the product of the heat capacity times the temperature difference) of the gaseous nitrogen rather than its latent heat of condensation is available for removing the cold of evaporation of the crude argon. As a result, the heat exchanger for crude argon evaporation must be relatively large in size. Furthermore, an amount of liquid equivalent to the quantity of crude argon withdrawn in the liquid phase must be fed into the rectification, and refrigeration must be additionally produced for this liquid at some other location.